Remove build constraints related to proto-lens.
Remove build constraints related to proto-lens.

Now that fpco/stackage-curator#64 has been merged, there is no longer
a conflict between the `protobuf-simple` package and `proto-lens`-related
packages.  Packages that use `proto-lens` to generate Haskell source files
should work now.  (I'm not sure whether we need to wait for a release of
`stackage-curator` before merging this.)

Changes:
- Allow `proto-lens-protobuf-types-0.3.0.2`; previously only older versions
  were allowed.
- Run tests for `proto-lens-combinators_test`; previously they were disabled.

I tested this change by running `stackage-curator` manually on the latest LTS,
(with `proto-lens-protobuf-types-0.3.0.1`) then rerunning the same commands
manually for `0.3.0.2` (ncluding recreating the PATH that `stackage-curator`
used).  But let me know if there are any other commands I can run to help
validate this.

mstksg/stackage,clinty/stackage,fimad/stackage,creichert/stackage,Shimuuar/stackage,spencerjanssen/stackage,wereHamster/stackage,peti/stackage,mgajda/stackage,stackbuilders/stackage,athanclark/stackage,mrkkrp/stackage,Daniel-Diaz/stackage,massysett/stackage,fpco/stackage,simonmichael/stackage,michalkonecny/stackage,ethercrow/stackage,int-index/stackage,soenkehahn/stackage,asr/stackage,jonschoning/stackage,iand675/stackage